Catheters have long been used for the treatment of diseases of the cardiovascular system, such as treatment or removal of stenosis. For example, in a percutaneous transluminal coronary angioplasty (PTCA) procedure, a catheter is used to insert a balloon into a patient's cardiovascular system, position the balloon at a desired treatment location, inflate the balloon, and remove the balloon from the patient. Another example is the placement of a prosthetic stent that is placed in the body on a permanent or semi-permanent basis to support weakened or diseased vascular walls to avoid closure or rupture thereof.
These non-surgical interventional procedures often avoid the necessity of major surgical operations. However, one common problem associated with these procedures is the potential release of embolic debris into the bloodstream that can occlude distal vasculature and cause significant health problems to the patient. For example, during deployment of a stent, it is possible for the metal struts of the stent to cut into the stenosis and shear off pieces of plaque which become embolic debris that can travel downstream and lodge somewhere in the patient's vascular system. Further, pieces of plaque material can sometimes dislodge from the stenosis during a balloon angioplasty procedure and become released into the bloodstream.
Medical devices have been developed to attempt to deal with the problem created when debris or fragments enter the circulatory system during vessel treatment. One technique includes the placement of a filter or trap downstream from the treatment site to capture embolic debris before it reaches the smaller blood vessels downstream. The placement of a filter in the patient's vasculature during treatment of the vascular lesion can collect embolic debris in the bloodstream.
It is known to attach an expandable filter to a distal end of a guidewire or guidewire-like member that allows the filtering device to be placed in the patient's vasculature. The guidewire allows the physician to steer the filter to a downstream location from the area of treatment. Once the guidewire is in proper position in the vasculature, the embolic filter can be deployed to capture embolic debris. Some embolic filtering devices utilize a restraining sheath to maintain the expandable filter in its collapsed configuration. Once the proximal end of the restraining sheath is retracted by the physician, the expandable filter will transform into its fully expanded configuration. The restraining sheath can then be removed from the guidewire allowing the guidewire to be used by the physician to deliver interventional devices, such as a balloon angioplasty catheter or a stent delivery catheter, into the area of treatment. After the interventional procedure is completed, a recovery sheath can be delivered over the guidewire using over-the-wire techniques to collapse the expanded filter (with the trapped embolic debris) for removal from the patient's vasculature. Both the delivery sheath and recovery sheath should be relatively flexible to track over the guide wire and to avoid straightening the body vessel once in place.
Another distal protection device known in the art includes a filter mounted on a distal portion of a hollow guidewire or tube. A moveable core wire is used to open and close the filter. The filter is coupled at a proximal end to the tube and at a distal end to the core wire. Pulling on the core wire while pushing on the tube draws the ends of the filter toward each other, causing the filter framework between the ends to expand outward into contact with the vessel wall. Filter mesh material is mounted to the filter framework. To collapse the filter, the procedure is reversed, i.e., pulling the tube proximally while pushing the core wire distally to force the filter ends apart. A sheath catheter may be used as a retrieval catheter at the end of the interventional procedure to reduce the profile of the “push-pull” filter, as due to the embolic particles collected, the filter may still be in a somewhat expanded state. The retrieval catheter may be used to further collapse the filter and smooth the profile thereof, so that the filter guidewire may pass through the treatment area without disturbing any stents or otherwise interfering with the treated vessel.
Sheath catheters may be of the “over-the-wire” variety with a guidewire lumen extending the entire length of the catheter, such that the guidewire is disposed entirely within the catheter except for the distal and proximal portions of the guidewire that protrude from the catheter. While these catheters are advantageous in many ways, exchanging the indwelling sheath catheter for another interventional or the retrieval catheter can be difficult often requiring multiple operators and the use of an exchange wire.
Sheath catheters may also be of the single operator or “rapid-exchange” type. A rapid-exchange sheath catheter typically includes a tubular body with a lumen extending the entire length thereof and a guidewire shaft having a guidewire lumen of minimal length positioned along a distal portion of the catheter, although some of these catheters are not advanced over guidewires at all. As such, the guidewire is located outside of the sheath catheter except for a short segment which runs within the guidewire lumen. As such, a clinician is able to control both ends of the guidewire while the sheath catheter is loaded onto the guidewire. The sheath catheter is then advanced through the patient with only a distal portion of the catheter “riding” on the guidewire.
While convenient for rapid and simple exchange, a rapid-exchange type sheath catheter sometimes lacks the desired stiffness and pushability for readily advancing the sheath catheter through the tortuous vascular system.
What is needed is a reliable sheath catheter that can be used with embolic filtering devices. The sheath catheter should be relatively easy for a physician to use and should provide an effective means for retrieving the filtering device without releasing any captured embolic debris into the body vessel. Moreover, the sheath catheter should be advance-able and removable from the guidewire in relatively quick fashion.